Conventionally, a throw-away cutting tool with a cutting insert attached to a holder has been used as a cutting tool for use in a cutting process or the like. The cutting insert used for the cutting tool generally includes an upper surface, a lower surface, and a side surface. A cutting edge is formed at an intersection of the side surface and at least one of the upper surface and the lower surface. The cutting edge is to be brought into contact with a workpiece being rotated so as to cut the workpiece.
As a cutting insert, Patent Document 1 has proposed a cutting tip having an upper surface thereof projections with which chips of a workpiece are brought into contact. The cutting insert described in Patent Document 1 is capable of curving the chips of the workpiece by bringing the chips into contact with a first projection (first ridge) and a pair of second projections (second ridges) respectively extending from the first projection.
However, with the cutting insert described in Patent Document 1, the chips are brought into contact with the second projections under conditions of large depths of cut, while the chips are not brought into contact with the second projections under conditions of small depths of cut. Moreover, in the cutting insert described in Patent Document 1, consideration is given to a change in depth of cut, but no consideration is given to a change in feed rate.
When the depth of cut is decreased and the feed rate is increased, the chips are easy to flow in a direction inclined from a bisector of a vertical angle. Therefore, the second projections are required to have a large inclination in order to facilitate curving of the chips during machining at small depths of cut and high feed rates. However, the increased inclination of the second projections may cause the problem that during machining at high feed rates, the durability of the second projections is deteriorated or chip packing is apt to occur.
Patent Document 1: Japanese Unexamined Patent Publication No. 2009-208216